1. Field of the Invention
This invention relates to improvements in monopolar batteries, and more particularly to providing electrical insulating elements in a monopolar cell.
2. Description of the Prior Art
In a monopolar cell, such as a lithium-alloy/molten salt/metal sulfide cell, the metallic cell case is typically in contact with one of the cell electrodes, usually the negative electrode. The positive electrode then must be electrically insulated from the metallic cell case. Ceramic materials such as boron nitride, aluminum nitride and magnesium oxide have been used as insulators, but they are relatively expensive. Moreover, if such ceramic insulators crack during assembly or use, the positive electrode may short to the cell case causing cell failure. Furthermore, cracks in the ceramic insulator may create electrolyte paths between the positive electrode and the cell case. If such cracks develop, lithium may be deposited between the positive electrode and the cell case during charging. Accordingly, there is a need for an improved insulator for a monopolar cell.
In patent application Ser. No. 08/234,070, now U.S. Pat. No. 5,476,734 filed Oct. 18, 1993, it was shown that a high melting point salt can be used to prevent the escape of electrolyte from bipolar cells and to prevent intercell leakage currents. A salt or salt mixture having a higher melting point than the electrolyte can be used to form a containment in the bipolar cell. The containment is placed adjacent the periphery of the cell components and may be provided as a packed powder, a fused or melted segment, or a flexible sleeve containing the higher melting point salt.